Look out, smartphone users: Bacteria may be after your rare earths. A microbe that lives in one of Earth’s harshest environments, sulfurous volcanic mud pits, needs one of several industrially valuable metals to make a vital enzyme. While rare earth elements have been found previously in plants and microbes, the mud-pit bacterium is the first organism known to need them for survival.

Methylacidiphilum fumariolicum makes its home in volcanic pools outside Naples, Italy, where it endures steami...